In a 2-inch deep, full-size steamtable pan, combine boiling water with sauce mix and butter. Whisk well to blend.
Add Classic Casserole® Scalloped Potatoes O’Brien Style potato slices and next 5 ingredients, mix thoroughly. Bake 35-40 min.
In sauté pan, heat oil over medium heat, add spinach leaves and sauté until tender. Remove from heat.
Remove potatoes from oven. Spread sautéed spinach evenly over potatoes and top with Monterey Jack. Bake for additional 10 min. or until cheese is melted. Serve or place in a steamtable to hold hot. Serve.